Minor cytotoxic cardenolide glycosides from the root of Streptocaulon juventas

• Six new minor natural cardenolide glycosides isolated from Streptocaulon juventas.
• Four cardenolide glycosides reported in this genus for the first time.
• One compound displayed cytotoxicity against A549 and NCI-H460 cell lines.
• Other compounds displayed different sensitivity against the two cell lines.

In order to determine new minor natural cardenolide glycosides as cytotoxic candidates, we isolated six new cardenolide glycosides together with four known ones, which had never previously been reported in the genus, by bioassay-guided separation from the 75% ethanol extract of Streptocaulon juventas (Asclepiadaceae). Their structures were elucidated on the basis of spectroscopic analysis, including homo- and heteronuclear correlation NMR experiments (COSY, HSQC and HMBC). The cytotoxic activities of these compounds were evaluated against A549 and NCI-H460 cell lines by MTT assay and compound 7 exhibited inhibitory activity against the two cell lines, while other compounds displayed a range of inhibitory activity against NCI-H460 and A549 cells. Their structure–activity relationships were also discussed.

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